The present application is a U.S. non-provisional application based upon and claiming priority from Japanese Application No. 2002-81105, with a filing date of Mar. 22, 2002, which is hereby incorporated by reference.
This disclosure relates to an economical method of recycling polycondensation resin waste. Polycondensation resins, such as polycarbonates, polyesters, polyamides, and polyarylates are materials with very a high economic value, currently being used in applications such as lenses, compact discs, construction materials, automobile parts, automobile chassis, office appliances, camera bodies, bottles, fibres, and the like. The demand for these resins is increasing. After use, the resins are often disposed of by burning them or burying them underground as waste. Recovery and recycling of these wastes is presently being examined from the viewpoint of environmental protection, economy, and reuse.
For example, some polycondensation resin wastes are used in partial remolding processes. Remolding, however, suffers from of lowering of the molecular weight, deterioration of physical properties such as strength, and discoloration of the material, all of which make large-scale reuse difficult. In addition, the material is usually discarded after only a single reuse. Thus, remolding is not recycling in the true sense.
Japanese Kokai Publication no. 6-220184 discloses a method of preparation of polycarbonate wherein polycarbonate waste is dissolved in monophenol and depolymerized (i.e., disintegrated) in the presence of a quaternary ammonium compound or quaternary phosphonium compound catalyst to form a mixture of oligocarbonate, diaryl carbonate and diphenol. The oligocarbonates obtained are then polycondensed.
Japanese Kokai Publication no. 7-316280 discloses a recycling method wherein the aromatic dihydroxy compounds or diaryl carbonates obtained by depolymerization of the aromatic polycarbonate resin waste were used as raw materials for the preparation of an aromatic polycarbonate resin. In this method, the aromatic dihydroxy compounds and diaryl carbonate compounds were recovered by a transesterification reaction between the aromatic polycarbonate waste and an aromatic monohydroxy compound, through the following steps. In Step 1, an aromatic polycarbonate resin and an aromatic monohydroxy compound were subjected to a transesterification reaction. In Step 2, the diaryl carbonate containing an aromatic monohydroxy compound was separated by distillation from the reaction product of Step 1. In Step 3, an aromatic monohydroxy compound was added to the aromatic dihydroxy compound left as residue in Step 2 and was heated to form an addition product, and the addition product was separated after deposition as crystals by cooling. In Step 4, the crystals obtained in Step 3 were heated and melted and the aromatic monohydroxy compound was distilled off to obtain an aromatic dihydroxy compound.
The methods described above, however, are disadvantegous in that the initially high molecular weight polymers are converted into oligomers or monomers using an energy-intensive process. This is particularly wasteful inefficient, since manufacture of the initial high molecular weight polymers is also an energy-intensive process.
Japanese Kokai Publication no. 11-152371 discloses a method of solid phase polymerization wherein the polycarbonate is not depolymerized. In this method, after dissolving the polycarbonate waste in a solvent, the dissolved polycarbonate component is crystallised. However, because this process requires solvent, it is not very satisfactory from the viewpoint of energy efficiency and environmental hygiene.
There thus remains a need for improved recycling methods for polycondensation resin waste.
The above-described and other drawbacks are alleviated by a method of producing a polycondensation resin comprising adding a polycondensation resin waste to a fusion polymerisation apparatus maintained at a temperature and a pressure effective to produce the polycondensation resin, wherein the polycondensation resin and the polycondensation resin waste are the same type of resin.
In another aspect, a method of producing a polycondensation resin comprises adding a polycondensation resin waste to a fusion polymerization apparatus, wherein the polycondensation resin waste is supplied from a polymerization reactor in which an oligomerization reaction is being performed to a reactor maintained at a temperature and a pressure effective to produce the polycondensation resin, wherein the polycondensation resin and the polycondensation resin waste are the same type of resin.
In yet another aspect, a method of producing a polycondensation resin comprises melting a polycondensation resin waste, adding a raw material monomer, an oligomer, a catalyst, or a combination comprising one or more of the forgoing materials to the polycondensation resin waste, and adding the polycondensation resin waste to a fusion polymerisation apparatus maintained at a temperature and a pressure effective to produce the polycondensation resin, wherein the polycondensation resin and the polycondensation resin waste are the same type of resin.